Update Modulefile, README, CHANGELOG for stdlib-4.0.0
Update function documentation for 4.0.0

Without this patch the function documentation is out of sync with the
functions contained in the standard library.  This commit updates the
functions.  I generated the list using this sequence:

    cd ~/src/puppet
    git checkout 3.1.1
    bundle exec puppet doc -r function > /tmp/puppet_functions.txt
    cd ~/src/stdlib
    bundle exec puppet doc -r function > /tmp/stdlib_functions.txt
    diff -U2 puppet_functions.txt stdlib_functions.txt | grep '^+' | perl -ple 's/^\+//' > functions.txt

I then replaced the README function documentation with the contents of
functions.txt which contains only the functions contained in stdlib.
Update gemspec for 4.0.0
Merge branch stdlib 4.0.0 release

* v4:
  Update gemspec for 4.0.0
  Update function documentation for 4.0.0
  Update Modulefile, README, CHANGELOG for stdlib-4.0.0